However, when PBMCs were cultured without human serum ("no serum supernatant") we observed that the SIRT1 concentration in the supernatant in IPF was significantly lower than the SIRT1 concentration of controls (1.97±0.59 ng/ml versus 2.4±0.74 ng/ml, respectively, p=0.047; Figure 1C). Here, SIRT1 is linked to idiopathic pulmonary fibrosis.